Pulse-modulated oscillation generator



June 1, 1948. D. L. SHAPIROI 2,442,514

PULSE-MODULATED 05 C I LLAT ION GENERATOR Fil ed Jan. 4, 194a INVENTOR: DAVID L. SHAPIRO,

ATT R N EY.

am June 1,

U NlTEl), STATES PATENT OFFICE PULSE-MODULATED OSCILLATION GENERATOR David L. Shapiro, Kew Gardens, N. Y., assignor, byvmesne assignments, to Hazeltine Research,

Inc., Chicago, 111., a corporation of Illinois Application January 4, 1946, Serial No. 639,086

14 Claims. (01. 179-1715) This invention relates, in general, to pulse-mod which means operating for a pulse interval that is short with reference to the time separation of the next succeeding pulse; In other words, a pulse of power is delivered during an interval short in a comparison with the period of the pulse-repetition frequency. For most installations, the generator is intended to function over a range of pulse-repetition frequencies which incidentally means .operation over a range of duty cycles since the value ofvthe duty cycle varies with the repetition frequency. While it is a simple matter to control the repetition frequency through the use of a. suitable pulse-modulation potential, it has been found that there is an undesirable tendency for the operating frequency of the generator to drift or deviate from a desired fixed value as the repetition frequency is varied over its range. This drift is attributable, in part, to the variations of heat, dissipation within the generator with changes in repetition rate or duty cycle. For example, the heating of the anode electrode of the oscillator tube or the heating of the frequencydetermining circuit, especially in oscillators including resonant cavities, has a pronounced effect on the operating frequency, and as such heating inherently tends to vary with the repetition rate it also tends to introduce a shift in the operating frequency.

Heretofore, it has been proposed to control the heat dissipation in a generator of the type under consideration through a thermal-transfer system fore, to provide a pulse-modulated oscillation gen.

erator which substantially avoids the aforementioned limitations of prior arrangements.

It is another objectof the invention to provide a pulse-modulated oscillation generator having an improved arrangement for maintaining substantially constant heat dissipation in at least a desired portion of the generator over a range of operating conditions.

It is a specific object of the invention to provide a pulse-modulated oscillation generator for operation over a range of pulse-repetition frequencies and having an improved frequency sta bility.

A pulse-modulated oscillation generator in accordance with the invention comprises an oscillatory circuit normally maintained in a predetermined operating condition and including an electron-discharge means having a cathode and at least one other electrode. The generator has means for producing a component of current between the cathode and other electrode to establish a corresponding component of heat dissipacurring in a manner determined by the modulat-- ing potential. Also, there is provided an integrating network having a time constant long with reference to the maximum separation of the timespaced pulses for modifying the aforesaid current component to maintain theaverage heat dissipation in the abovementioned portion of the oscillatory circuit substantially constant during operating intervals of pulse modulation long with respect to the separation of the time-spaced pulses.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawingand itsscope will be pointedout in the appended claims.

In the drawing, Fig. 1 is a schematic circuit diagram of a pulse-modulated oscillation generator embodying the invention in one form: and Fig. 2 is a schematic circuit diagram of a similar oscillator including the invention in modified form.

Referring now more particularly to Fig. 1, the arrangement there represented constitutes a pulse-modulated oscillation generator for operation over a range of repetition frequencies and embodying the present invention to maintain a substantially constant anode dissipation, as averaged over operating intervals of pulse modulation. The generator comprises an oscillatory circuit normally maintained in a predetermined operating condition and including an electron-discharge means having a cathode and at least one other electrode. This oscillatory circuit is provided by a triode-type vacuum tube l having an anode, a cathode and control electrode and an associated frequency-determining circuit, repre... sented by an inductor II, and a condenser 2. While the frequency-determining circuit may take the form of a resonant cavity, transmissionline section or similar high-frequency resonantcircuit unit having distributed inductance and capacitance, lumped reactance elements have been illustrated in the schematic circuit diagram. These elements may be individually or simultaneously adjustable to achieve a desired operating frequency in the generator. Condensers i3 and I4 serve to couple the frequency-determining circuit to the anode and control electrodes, respectively, of tube ill. The cathode of this tube is coupled to the frequency-determining circuit by way of a capacitive-type voltage divider, provided by condensers l5 and is shown in brokenline construction since the comprise interelectrode capacitances of the tube electrodes. The cathode is grounded through a radio-frequency signal choke l1 and the control electrode is likewise grounded through a similar choke l8 and a resistor l9, completing an oscillatory circuit of the well-known Colpitts type. This circuit is normally maintained in a nonoscillatory condition.

In order to facilitate controlling heat dissipation in a particular portion of the described oscilliatory circuit, the generator has means, in-

cluding a source of unidirectional potentiahfor producing a component of direct current between the cathode and some other electrode of tube ID to establish a corresponding component of heat dissipation in the particular portion of .the

oscillatory circuit. This means comprises a normally conductive trlode-type vacuum tube 25 having anode, cathode and control electrodes. A source of space current, shown as a battery 26, is coupled to the output electrodes of tube 25 and a second battery 21-is associated with its input electrodes, applying a bias potential of positive polarity to its control electrode. For the embodiment under consideration, this tube is to control heat dissipation" at the anode electrode of oscillator tube l0. To this end, its output circuit includes the anode-cathode path of tube In so that a component of anode-cathode current is established in tube I0 in accordance with the conductivity of tube 25.

Pulse-modulated'operation of the oscillation generator is accomplished through a pulse transformer 30, constituting means for applying a periodically repeating pulse-modulating potential to the oscillatory circuit to control the circuit to generate a modulated carrier-wave signal having time-spaced pulses occurring in a manner determined by the applied modulating potential. The primary winding of transformer 30 is connected with input terminals 3| and 32 for re-' ceiving a suitable modulating potential. Its secondary winding is coupled directly to the anode and cathode electrodes of tube I!) through a condenser 33. The modulating potential is isolated from tube 25 through a filter provided by an inductor 34 and a shunt-connected condenser 35. The direct current componentof tube 25, in

4 turn. is isolated from the secondary winding of the pulse transformer through a resistor 30 which has a high impedance with reference to the normal impedance of the anode-cathode circuit of tube I0.

The generator further includes integrating means, responsive to the applied modulating potential, for modifying the magnitude of the an-- ode-cathode current component or tube Ill contributed by tube 25 to maintain the average heat dissipated at its anode electrode substantially constant during operating intervals of pulse modulation long with respect to the separation of the generated pulses. The integrating means comprises the parallel combination of a resistor 40 and a condenser 4|, connected across the secondary winding of the pulse transformer through a series resistor 42 and a diode rectifier 43. Resistor 40 and condenser 4| are selected so that .the integrating circuit has a time constant which is long with reference to the period of the lowest pulse-repetition frequency, contemplated. The control voltage developed by the integrating circult is applied through a filter, comprising an inductor 44 and a condenser 45, to the control electrode of tube 25 in opposition with the potential of the bias source 21. Preferably, the generator is so adjusted that the direct current component established between the anode and cathode electrodes of tube l0 due to the conductivity of tube 25 produces a fixed heat dissipation at the anode of tube I0 without initiating oscillations in the oscillatory circuit, Also, the value of bias source 21 may be selected to equal the maximum voltage developed by integrating circuit 40, 4| in response to an applied periodic pulse-modulating potential of the highest repetition frequency to be encountered. Additionally, condenser 23 is of such size that it does not charge appreciably within the duration of any applied modulating pulse and discharges substantially completely in the interval between succeeding modulating pulses.- An output signal may be derived from the generator and supplied to a utilizing device (not shown) coupled to output terminals 41, 48 by an inductor 46 magnetically coupled with the frequencydetermining circuit ll, l2.

In considering the operation of the described arrangement, it will be assumed initially that a repeating pulse-modulated potentialof a fixed repetition frequency is applied to terminals ll, 32. Each pulse of the modulating potential initiates oscillations in the oscillatory circuit which endure for the duration of the applied pulse, thereby generating a single pulse of an output signal. Thus, with an applied periodically repeating modulating potential the generator is controlled to produce a modulated carrier-wave signal having time-spaced pulses, occurring at a pulse-repetition frequency corresponding to that of the modulating potential. In the intervals between the generated pulses a direct current component flows between the anode and cathode of tube In by virtue of its location in the output circuit of tube 25. The magnitude of this current component is adjusted in accordance with the repetition frequency oi, the modulating pulses which are rectified by diode 43, deriving in the integrating circuit 40, 4| a control effect or voltage of negative polarity having a magnitud which varies directly with the pulse-repetition frequency. This negative potential opposes that of bias source 21 and controls the conductivity of tube 25, thereby adJusting the magnitude of electrode.

its output signal inversely in accordance with the repetition frequency of the modulating potential. 1% high repetition frequencies which produce high heat dissipation at the anode of tube ill in response to the generation of the time-spaced pulses, the integrating circuit causes tube 25 to be driven in the direction of anode current cutoff. This reduces the direct current component of tube II) in the intervals between its generated pulses and establishes a certain average heat dissipation at the anode of tube l over operatin intervals of pulse modulation long with respect to the time separation of the generated pulses. At low pulse-repetition frequencies, on the other hand, tube 25 produces an increased direct current component in tube l0, increasing the dissipation at the anode thereof during the intervals between the generated pulses. The change in magnitude of this direct current component, being inversely related to the repetition frequency, causes substantially the same average heat dissipation to occur at the anode for all pulserepetition frequencies within the desired operating'range. By maintaining the average heat dissipation substantially constant in this fashion,

frequency drift which may otherwise be experienced due tothe variation of anode heat dissipation with repetition frequency are substan tially eliminated.

Tube III has been described as being included 'in an oscillatory circuit that is normally maintained in' a nonoscillatory condition. However, if desired, the operating potentials applied to the tube may be chosen so that in the absence of modulating potentials at terminals 3|, 32 the circuit generatesa continuous wave signal of low amplitude. The advantage obtained is that the circuit, if normally generating such a signal, responds more rapidly to modulating potentials applied through transformer 30 than otherwise.

This accelerated response is highly desirable for some applications.

The oscillation generator of Fig. 2 is generally similar to that of Fig. 1, corresponding components thereof being identified by the same reference characters. The generator of Fig. 2 is normally maintained in a nonoscillatory condition but, in the absence of an applied modulating potential, components of direct current flow to anode and cathode electrodes of the tube through the ,secondary winding of the pulse transformer and a radio-frequency signal choke 5|. The current component to the control electrode is produced by a further potential source 52 which applies an operating bias of positive polarity to this The oscillator of Fig. 2 also includes means for stabilizing its operating frequency with variations in duty cycle, this means comprising the integrating circuit 40, 4| which, here, is positioned in the cathode circuit of tube In.

The operation of the Fig. 2 arrangement is generally similar to that of Fig. 1. However, in Fig. 2 the control voltage developed by the integrating circuit 40, M in response to the pulsemodulated operation of the oscillation generator applies an operating bias which modifies both the anode current and control-electrode current components of tube l0. These cin'rent components are varied inversely with the pulse-repetition frequency of the applied modulating potential to maintain substantially constant average heat dissipation at both the anode and control electrodes during operating intervals of pulse modulation which are long with reference to the separation of the generated pulses. Resistors l9 and 40 are variable to enable the anode current and controlelectrode current components to be adjusted. In this circuit arrangement, the grid current of tube I0 produces a damping eifect on the oscillatory circuit to preserve its nonoscillatory condition in the absence of a modulating potential at terminals 3|, 32.

While the described generators have been considered in connection with applied modulating potentials of fixed repetition frequencies, it will be apparent theta compensation for variation in the heat dissipation at particular portions of the oscillatory circuit with variations in duty cycle is obtained even though the modulating potential does not recur at fixed repetition frequencies. Such compensation may be realized by selecting the time constant of the integrating circuit 40. H to be long with'reference to the maximum separation of the time-spaced pulses produced in the generators under the control of the applied modulating potentials.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A pulse-modulated oscillation generator comprising, an oscillatory circuit normally maintained in a predetermined operating condition and including an electron-discharge means having a cathode and at least one other electrode. means for producing a component of current between said cathode and said other electrode to establish a corresponding componentof heat dissipation in a particular portion of said oscillatory circuit, means for applying a repeating pulsemodulating potential to said oscillatory circuit to control said circuit to generate a modulated carrier-wave signal having time-spaced pulses occurring in a manner determined by said modulating potential, and an integrating network having a time constant long with reference to the maximum separation of said pulses for modifying said current component to maintain the average heat dissipation in said portion of said circuit substantially constant during operating intervals of pulse modulation long with respect to the separation of said pulses.

2. A pulse-modulated oscillation generator comprising, an oscillatory circuit normally maintained in a nonoscillatory condition and including an electron-discharge means having a cathode and at least one other electrode, means for producing a component of current between said cathode and said other electrode to establish a corresponding component of heat dissipation in a particular portionof said oscillatory circuit without initiating oscillations therein. means for ap plying a repeating pulse-modulating potential to said oscillatory circuit to initiate oscillations therein and generate a modulated carrier-wave signal having time-spaced pulses occurring in a manner determined by said modulating potential. and an integrating network having a time constant long with reference to the maximum separation of said pulses for developing a control potential to modify said current component to maintain the average heat dissipation in said 7 portion of said circuit substantially constant during operating intervals of pulse modulation long with respect to the separation oi. said pulses.

3. A pulse-modulated oscillation generator comprising, an oscillatory circuit normally maintained in a predetermined operating condition and including an electron-discharge means having a cathode and at least one other electrode, means for producing a component of direct current between said cathode and said other electrode to establish a corresponding component of heat dissipation in a particular portion of said oscillatory circuit, means for applying a repeating pulse-modulating potential to said oscillatory circuit to control said circuit to generate a modulated carrier-wave signal having time-spaced pulses occurring in a manner determined by said modulating potential, and an integrating network having a time constant long with reference to the maximum separation of said pulses and associated with said means producing said component to direct current for modifyin said current component to inaintain the average heat dissipation in said portion of said circuit substantially constant during operating intervals of pulse modulation long with respect to the separation oi said pulses.

4. A pulse-modulated oscillation generator comprising, an oscillatory circuit normally maintained in a predetermined operating condition and including an electron-discharge means having a cathode and at least one other electrode, means including a source of unidirectional potential coupled between said cathode and said other electrode for producing a component of current therebetween to establish a corresponding component of heat dissipation in a particular portion of said oscillatory circuit, means for applying a repeating pulse-modulating potential to said oscillatory circuit to control said circuit to generate a modulated carrier-wave signal having.

time-spaced pulses occurring in a manner determined by said modulating potential, and an integrating network having a time constant long with reference to the maximum separation of said pulses for developing a potential opposing said unidirectional potential to modify said current component to maintain the average heat dissipation in said portion of said circuit substantially constant during operating intervals of pulse modulation long with respect to the separation of said pulses.

5. A pulse-modulated oscillation generator comprising, an oscillatory circuit normally maintained in a predetermined operating condition and including an electron-discharge means having a cathode and at least one other electrode, means for producing a component or current between said cathode and said other electrode to establish a corresponding component of heat dissipation in a. particular portion of said oscillatory circuit, means for applying a periodically repeating pulse-modulating potential to said oscillatory circuit to control said circuit to generate a modulated carrier-wave signal having time-spaced pulses occurring with a repetition frequency determined by said modulating potential, and an integrating network having a time constant long with reference to the maximum separation of said pulses for varying the magnitude of said current component inversely with the repetition frequency 01' said pulses to maintain the average heat dissipation in said portion of said circuit substantially constant during operating intervals 8 of pulse modulation long with respect to the separation of said pulses.

6. A pulse-modulated oscillation generator for operation over a range of pulse-repetition frequencies comprising, an oscillatory circuit normally maintained in a predetermined operating condition and including an electron-discharge means having a cathode and at least one other electrode, means for producing a component of current between said cathode and said other electrode to establish a corresponding component oi heat dissipation in a particular portion of said oscillatory circuit, means for applying a period ically repeating pulse-modulating potential to said oscillatory circuit to control said circuit to generate a modulated carrier-wave signal having time-spaced pulses occurring with a repetition frequency determined by said modulating potential, and an integrating network having a time constant long with respect to the period of the lowest repetition frequency within said range for developing a control potential to modify said current component to maintain the average heat dissipation in said portion of said circuit substantially constant during operating intervals of pulse modulation long with respect to the separation of said pulses.

7. A pulse-modulated oscillation generator comprising, an oscillatory circuit normally maintained in a predetermined operating condition and including an electron-discharge means having a cathode and at least one other electrode, means for producing a component of current between said cathode and said other electrode to establish a corresponding component of heat dissipation in a particular portion of said oscillatory circuit, means for applying a repeating pulsemodulating potential to said oscillatory circuit to control said circuit to generate a modulated carrier-wave signal having time-spaced pulses occurring in a manner determined by said modulating potential, and an integrating network having a time constant long with reference to the maximum separation of said pulses and responsive to said modulating potential for developing a control potential to modify said current component to maintain the average heat dissipation in said portion of said circuit substantiall constant during operating intervals of pulse modulation long with respect to the separation of said pulses.

8. A pulse-modulated oscillation generator comprising, an oscillatory circuit normally maintained in a predetermined operating condition and including an electron-discharge means having at least an anode and a cathode, means for producing a component of current between said anode and cathode to establish a corresponding component of heat dissipation in a particular portion of said oscillatory circuit, means for applying a repeating pulse-modulating potential to said oscillatory circuit to control said circuit to generate a modulated carrier-wave signal having time-spaced pulses occurring in a manner determined by said modulating potential, and an integrating network having a time constant long with reference to the maximum separation of said pulses for developing a control ell'ect to modify said current component to maintain the average heat dissipation in said portion of said circuit substantially constant during operating intervals of pulse modulation long with respect to the separation of said pulses.

9. A pulse-modulated oscillation generator comprising, an oscillatory circuit normally maintained in a predetermined operating condition and including an electron-discharge means having at least an anode and a cathode, vacuum-tube means having an output circuit including said anode and cathode of said electron-discharge means for producing a component of current therebetween to establish a corresponding component of heat dissipation at said anode, means for applying a repeating pulse-modulating potential to said oscillatory circuit to control said circuit to generate a modulated carrier-wave signal having time-spaced pulses occurring in a manner determined by said modulating potential, and an integrating network having a time constant long with reference to the maximum separation of said pulses for controlling the conductivity of said vacuum-tube means to modify said current component and maintain the average heat dissipation in said portion of said circuit substantially constant during operating intervals of pulse modulation long with respect to the separation of said pulses.

10. A pulse-modulated oscillation gfi lerator comprising, an oscillatory circuit normally maintained in a predetermined operating, condition and including an electron-discharge means having at least an anode and a cathode, vacuum-tube means having an output circuit including said anode and cathode of said electron-discharge means for producing a component of current therebetween to establish a corresponding component of heat dissipation at said anode, means for applyins a repeating pulse-modulating potential to said oscillatory circuit to control said circuit to generate a modulated carrier-wave signal having time-spaced pulses occurring in a manner determined by said modulating potential, an integrating network having a time constant long with reference to the maximum separation of said pulses for integrating said modulating potential to derive a control effect, and means for utilizing said control eflect to control the conductivity of the vacuum-tube means to modify said current component and maintain the average heat dissipation at said anode substantially constant during operating intervals or pulse modulation long with respect to thevseparation of said pulses.

11. A pulse-modulated oscillation generator comprising, an oscillatory circuit normally maintained in a predetermined operating condition and including an electron-discharge mean having anode, cathode and control electrodes, means for producing a component of current between said cathode and said control electrode to establish a corresponding component of heat dissipation at said control electrode, means for applyin a repeating pulse-modulating potential to said oscillatory circuit to control said circuit to generate a modulated carrier-wave signal having timespaced pulses occurring in a manner determined by said modulating potential, and an integrating network having a time constant long with reference to the maximum separation of said pulses for developing a control potential to modify said current component to maintain the average heat dissipation at said control electrode substantially constant during operating intervals 01 pulse modulation long with respect to the separation of said pulses.

12. A pulse-modulated oscillation generator comprising, an oscillatory circuit normally maintained in a predetermined operating condition and including an electron-discharge means having anode, cathode and control electrodes, means for producing components of current between said cathode and anode electrodes and between said cathode and control electrodes to establish corresponding components of heat dissipation at said anode and control electrodes, means for applying a repeating pulse-modulating potential to said oscillatory circuit to control said circuit to generate a modulated carrier-wave signal having time-spaced pulses occurring in a manner determined by said modulating potential, and an integrating network having a time constant long with reference to the maximum separation of said pulses for developing a control potenial to modify said current components to maintain the average heat dissipation at said anode and control electrodes substantially constant during operating intervals of pulse modulation long with respect to the separation of said pulses.

13. A pulse-modulated oscillation generator comprising, an oscillatory circuit normally maintained in a predetermined operating condition and including an electron-discharge means having a cathode and at least one other electrode, means for producing a component of current between said cathode and said other electrode to establish a corresponding component of heat dissipation in a particular portion of said oscillatory circuit, means for applying a repeating pulsemoclulating potential to said oscillatory circuit to control said circuit to generate a modulated carrier-wav signal having time-spaced pulses occurring in a manner determined by said modulating potential, and an integrating network included in the cathode circuit of said electron-discharge means and having a time constant long with ref- I erence to the maximum separation 01 said pulses for developing a control potential to modify said current component to maintain the average heat dissipation in said portion of said circuit substantially constant during operating intervals of pulse modulation long with respect to the separation of said pulses.

14. A pulse-modulated oscillation generator comprising, an oscillatory circuit normally maintained in a predetermined operating condition and including an electron-discharge means having a cathode and at least one other electrode, means for producing a component of current between said cathode and said other electrode to establish a corresponding component of heat dissipation in a particular portion of said oscillatory circuit, means for applying a repeating pulsemodulating potential to said oscillatory circuit to control said circuit to generate a modulated carrier-wave signal having time-spaced pulses occurring in a manner determined by said modulating potential, and means for stabilizing the operating frequency of said generator including an integrating circuit having a time constant long with reference to the maximum separation 0! said pulses for developing a control effect to modify said current component to maintain the average heat dissipation in said portion of said circuit substantially constant during operating intervals of pulse modulation long with respect to the separation of said pulses.

DAVID L. SHAPIRO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,003,285 Ditcham June 4, 1935 2,338,512 Harmon Jan. 4, 1944 

